1. Field of the Invention
The present invention relates to a stacked variable inductor, in particular to the inductor that can have variable inductance by using MOSFETs and inductors formed on two or more than two different layers in a CMOS structure having a plurality of metal layers.
2. Description of the Prior Art
RF blocks of recent RF IC technology has become more complicated to accommodate various services such as 900 MHz cellular, 1.5 GHz GPS, 1.9 GHz PCS, 2.4 GHz Blue-tooth, 5.2 GHz WLAN. This occurs because that a carrier frequency of each service is different so that transmitting/receiving circuit that is to be processed should be changed in accordance with each band of the carrier frequency. The most part that is changing from the transmitting/receiving circuit in accordance with a different carrier frequency is an impedance matching circuit.
An inductance matching circuit usually consists of inductors and capacitors, and an integrated inductor and capacitor are commonly used, but an integrated variable inductor is hardly used. When the integrated variable inductor and capacitor are available, input/output impedance in an amplifying circuit can be matched to several carrier frequencies, and signals of double or multi band can be processed with one amplifier so that transmitting/receiving terminals can be made with ease.
Hereinafter, inductors implemented by the prior art will be explained with reference to the accompanying drawings.
First of all, a stacked inductor in accordance with the prior art will be explained with reference to FIG. 1. Metal wirings 111, 112, 113 wound in coil form are connected to a port 1 and port 2 so that an inductor is formed. A stacked inductor using such multi layered wiring technology uses a stacked structure by connecting inductors 111, 112, 113 having small area in serial in order to reduce its area while maintaining high inductance.
However, this variable inductor has disadvantage that parasitic capacitance presenting between stacked inductors causes a resonance frequency fres low to be 0.9˜1.8 GHz so that the inductor can not be used above the resonance frequency and it's impedance can not be varied.
Next, as shown in FIG. 2, an inductor of the prior art includes an inductor for DC bias. This inductor is formed with single layer and occupies large area, so that it's impedance cannot be variably used.
FIG. 3 shows a variable active inductor of the prior art. In the prior art, an active inductor takes the most part of integrated variable inductor technology, which has characteristics that it can vary its inductance by having the equivalent configuration as the inductor shown in FIG. 3. This scheme has an advantage of having high quality factor. However, additional power consumption is required for the inductor and the inductor cannot be applied for frequency above 1˜2 GHz.
Therefore, an example of variable inductor using switches and multi metal CMOS technology among disclosed variable inductor up to the present time does not exist.